The invention relates to platelet-shaped pigments having high covering power and high luster. A satisfactory covering or hiding power and luster at the same time can often only be obtained with difficulty in the case of platelet-shaped pigments. Thus, mica substrates which are coated, for example, with one or more thin metal oxide films, are distinguished by interference colors and high luster but at the same time also by high transparency, due to the transparent substrate, and thus by a comparatively low covering power. Although the covering power can be improved by using colored metal oxide films composed, for example, of chromium oxide or iron oxide, even the covering power of pigments of this type of ten does not meet all requirements. The covering power can be further increased by depositing relatively rough metal oxide films on the pigments. The increased number of scattering centers increases the covering power but diminishes the luster. Furthermore, it has been proposed to use plate-shaped metal substrates, resulting in pigments of a very high covering power. On the other hand, this simultaneously results in a very hard metallic luster, which is often aesthetically not completely satisfactory. Additionally, it was observed that when extruding, for example, a polymer containing metal flakes, the metal flakes do not necessarily orient in parallel to each other but form complicated textures what results in a decreased covering power of the extruded polymer.
Accordingly, there was a high demand for platelet-shaped pigments which are distinguished by high luster, high covering power and high aesthetic appeal and which enlarge and supplement the range of available platelet-shaped pigments.
The specification of copending U.S. patent application Ser. No. 07/834,960, by the same inventors, relates to pigments containing carbon black which are calcined in the absence of oxygen and which is hereby incorporated by reference herein.